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Unaudited Quarterly Operating Results
12 Months Ended
Dec. 31, 2013
Unaudited Quarterly Operating Results [Abstract]  
Quarterly Financial Information [Text Block]
(20)    Unaudited Quarterly Operating Results (in millions)

 
 
Three-Month Periods Ended
 
 
March 31,
 
June 30,
 
September 30,
 
December 31,
 
 
2013
 
2013
 
2013
 
2013
 
 
 
Operating revenue
 
$
1,232

 
$
1,215

 
$
1,398

 
$
1,302

Operating income
 
297

 
311

 
389

 
267

Net income
 
160

 
166

 
216

 
140


 
 
Three-Month Periods Ended
 
 
March 31,
 
June 30,
 
September 30,
 
December 31,
 
 
2012
 
2012
 
2012
 
2012
 
 
 
Operating revenue
 
$
1,191

 
$
1,153

 
$
1,327

 
$
1,211

Operating income
 
278

 
251

 
378

 
114

Net income
 
151

 
130

 
212

 
44